Internal combustion engine with piston having combustion cavity in its head



Jan. 27, 1959 A. J. MORRIS 2,870,754

INTERNAL COMBUSTION ENGINE WITH P ON HAVING COMBUSTION CAVITY IN ITS DFiled June 21, 1954 2 Sheets-Sheet 1 Jan. 27, 1959 A. J. MORRIS2,870,754

INTERNAL COMBUSTION ENGINE WITH PISTON HAVING COMBUSTION CAVITY IN ITSHEAD Filed June 21, 1954 V 2 Sheets-Sheet 2 ,2 Z/I 10b (96' j g 106' & 915 0 6a Inventor m Alberto Jorge Morris United States Patent INTERNALCOMBUSTION ENGINE WITH PISTON HAVING COMBUSTION CAVITY IN ITS HEADAlberto Jorge Morris, Dnrsley, England, assignor to Lister & CompanyLimited, Dursley, England, a British company Application June 21, 1954,Serial No. 438,198 Claims priority, application Great Britain May 3,1951 22 Claims. (Cl. 123-32) This invention relates to pistons of thetype, hereinafter referred to as thetype specified, used in internalcombustion engines and formed with a combustion-space cavity in thepiston head, the wall of the cavity being undercut around the peripheryof an inlet orifice to the cavity, and also relates to engines employingpistons of the type specified.

This invention is concerned with improvements in pistons of the typespecified and in engines employing such pistons, and the features ofimprovement are directed to improving combustion of fuel or to avoidingdisadvantages in the manufacture or use of pistons of the typespecified.

According to the present invention, there is provided aupiston of thetype specified, wherein the inlet orifice to the cavity is formed by athroat tapering inwards towards the cavity, and wherein the wall of thecavity has a peaked land projecting from the bottom of the cavitytowards the inlet orifice and has its surface formed as a surface ofrevolution whereof the axis of revolution is coaxial with said land andwith the inlet orifice and whereof the generatrix is a line having agreater radius of curvature adjacent the land than adjacent the inletorifice.

According to a feature of the invention, the generatrix of thewall is aportion of a spiral, or is formed by two arcs of difierent radii-ofcurvature with the centre of curvature of the larger radius arc ofisetfrom the axis of revolution by an amount equal to the radius of the arcand with the centres of curvature of the arcs spaced apart bya distanceequal to the difference in length of the radii of curvature so that thesmaller radius arc is a continuation of the outer end of the largerradius arc, the smaller radius are forming part at least of the cavityWall immediately surrounding the inlet orifice and the larger radius areforming part at least of the cavity Wall opposite the orifice.

The peaked land may be rounded otf to have its truncated apex at adistance of about two-fifths of the radius of the larger are below theplane containing the loci of the centres of the arcs. Alternatively, theapex can be flattened, or can be formed with a depression facing theorifice, or can be provided with a' mushroom-shaped head.

According to yet another feature of this invention the diameter of theorifice giving access to the cavity 1n a piston of the type specifiedmay be made small compared with the diameter of the piston. Preferablythe ratio of the diameters lies within the range 0.15:1 and 0.25:1.

According to yet another feature of the invention, the inlet orificegiving access to the cavity in the piston may have the final entryportion of the inlet orifice tapered at an included angle of Accordingto yet another feature of the invention, to facilitate manufacture ofthe piston the orifice giving access to the cavity and the portion ofthe cavity wall immediately surrounding the orifice to the cavity may beformed by a ring secured in a threaded outer end of a sired, theopposite surface seating on the bottom of the recess over part only ofits area, the bottom of the recess being for instanceformed with aperipheral seating land.

Some embodiments of this invention will now be described with referenceto the accompanying diagrammatic drawings in which- Figure l is an axialsection through an engine cylinder fitted with a piston of the typespecified which embodies a number of novel features according to thisinvention.

Figure 2 is a view of the head of the piston illustrating other featuresof this invention,

Figure 3 is a view corresponding to Figure l of a modification,

Figure 4 is a view of a modification of the arrangement shown in Figure3, and

Figure 5 is an axial section of an arrangement employing a spiralgeneratrix for the wall of the cavity.

Referring to the drawings, the engine comprises a cylinder 1 having acentre line 11:, a cylinder head 2 having formed therein a bore 4 toreceive a fuel injector, the bore having a centre line 4a which isinclined to the centre line 1a but which is contained in a planecontaining thecentre line 1a and indicated in Figure 2 by the line 41;,an air inlet duct 6 which terminates in an air inlet port 5, thepositions of these parts being indicated at Figure 2 showing that theair inlet port 5 and the air inlet duct 6 are so positioned that airentering the cylinder is given a rotary motion, as indicated by arrow 7,

about the axis 1a of the cylinder, and a piston 3 which is flat-toppedand has a cavity 8 formed in the head to afford a combustion space forthe fuel being injected into the engine cylinder. I

Access to the cavity 8 is obtained through an orifice 9, and the cavity8 and orifice 9 are bounded by walls 8b, 10b and 9a which are surfacesof revolution about an axis 8a, the wall of the cavity being undercut asshown around the periphery of the orifice 9. The cavity 8 is bounded bywalls 8b and 10b which are both surfaces of revolution of arcs ofcircles, the centre 8c of the arc for forming the wall 8b being offsetfrom the axis 8 1 by an amount equal to the radius of the are forforming the wall 812, and the centre 10c of the are for forming the wallportion 1%, which are is of less radius of curvature than that for thewall part 8b, being disposed in the plane of the locus of the centresand on the side of the centre remote from the axis 8a, the centres 8cand 10c being spaced apart by a distance equal to the difference in theradii of curvature of the arcs for forming the walls 8b and 10b. Thusthe ends of the arcs for forming the Walls 8b and 101) remote from theaxis 8a meet in a common tangent.

By reason of the centre 8c being a distance from the axis 8a equal tothe radius of the are for forming the wall 8b there is formed at thecentre of the cavity an upstanding land 11. In Figures 1 and 3, thelandis peaked and is rounded off so as to terminate at a distance belowthe plane containing the centres 80 and 10c equal to about two-fifths ofthe radius of the are for forming the wall 812. In Figure 4 the land 11is flattened and supports a peaked button 14 the purpose of which willbedescribed more fully below.

The orifice 9 giving access to the cavity 8 is formed as a taperingthroat, the entrance portion of the throat being rounded and the finalinlet portion of the throat 9a being a cone having an apex angle of say15. I

'The tapering form of the orifice 9 causes acceleration of the gasesflowing through the orifice 9 into the cavity 8 i th form Q he cavity su hat very u bu nt .1 ditions a fe'c reated within the cavity 8.

The orifice 9 has a throat diameter which is small compared with thediameter of the piston 3. The ratio of the diameter of'the tbroat at thenarrowest point to the piston diameter is conveniently within the range0.15:1 and 0.25:1. The restricted form of the orifice 9, also assists inaccelerating the gas flow into the cavity 8 and assists in increasingturbulence therein.

As will be seen from Figure 2, the axis 8a, which is indicatedin Figure2 by point A, is offset from the plane 417 containing the axis of thecylinder 14 and the axis 4a of the fuel injector bore and the amount bywhich it is offset is selected to accommodate for deflection of the fuelSpray angularly with respect to the centre line In caused by the swirl(represented by arrow 7) of the gases entering-the cylinder through port5. As will also be seen from Figure 2 the 8a is offset from the planethrough axis In at right angles to th Plane 4b, the amount by which itis offset from this plane being selected so that fuel being injectedinto the cylinder can pass into the cavity 8 without impinging on thewalls of the orifice 9.

In each of the arrangements illustrated, the wall portion 101 and theorifice 9 are aiforded by a ring 10 threaded into the outer end of arecess cast or otherwise formed in the head of the piston 3; thisarrangement facilitates manufacture of the piston. The ring lflneed notbe of the samematerial as the piston 3, for instance the ring 10 may bemade from a more heat-resistant material, for instance a ceramicmaterial, than the piston 3, or may be coated with a' highlyheat-resistant material such as a ceramic material.

The wall portion 8b of the cavity 8 and the land 11 may be formed in anumber of ways. Thus, referring to Figure l, the bottom of the recess isshaped to afford the wall portion 81) and the land 11, and also toafford a shoulder 12 against which the ring 10 abuts when it is threadedinto the recess.

Referring to Figures 3 and 4, the recess is substantially a cylindricalrecess, and the wall portion 85 and land 11 areprovided by insertinginto the bottom of the recess a disc-like insert 15 having a suitableupper surface; the under surface of the insert 15 bears against thebottom of the recess an dto assist to insulate the piston head from thecavity 8, the insert '15 is arranged to bear against the bottom of therecess over part only of its under surface, there being a peripheralseating land 16 around the bottom of the recess. The insert 15 ispreferably made from a highly heat-resistant material and may forinstance be made from a ceramic material and thus further insulate thecavity 8 from the piston head.

Referring now to Figure 4, the button 14 is made from a highlyheat-resisting material and is a solid of revolution about the axis 8a.The button has a mushroomshaped head and has a maximum diameter of about0.15 to 0.25 times the diameter of the piston. The button is shapedtodeflect the fuel spray impinging on it in an upward direction towardsthe surface 10b. The periphery of the button overhangs the land 11 andthus any fuel running down the surface of the button will fall into aturbulent zone adjacent the button periphery. The summit of the buttonis roughly level with the plane containing the centres :80, 100. Thebutton 14 may as illustrated be formed separately from the insert 15 andattached thereto as by a rivet stem 14a, or may be made integral withthe insert 15.

The button 14 assists in reducting ignition lag and combustion noise byimproving mixing of the fuel and air in the cavity,.a nd by retainingheat assists in ignition.

The button arrangement is especially useful in small eng nes It ispreferably arranged as shown for the centre line of; the fuel spray toimpinge on the apex of the land within a circleconcentric with thecavity and having aradius equal to 0.1r, where r is the radius of thelarger radiussed arc'ofgen'er'atriii of the cavityf" i Instead of thegeneratrix of the cavity 8 consisting of two circular arcs, it may takethe form of a spiral 17 as shown in Figure 5, the spiral increasing inradius of curvature from adjacent the orifice to adjacent the land. Thearrangements of Figures 1 to 4 are however preferred since the machiningis rendered easier.

I claim:

1. An internal combustion engine piston having. a piston head, whereofthe'end surface affords the,crown of the piston, a combustion cavity inthe piston head, an entry throat of circular section-open at one end tothe ro of h pis a d at t opposi e end t t e av ty said throat taperingfrom the crown to the cavity whereby gases entering the combustioncavity are accelerated in their passage through the throat, said cavityhaving its wall opposite the entry throat forme d with a peaked landwhich projects, towards the entry throat coaxialiy there- ,with, thewall",of thecavity being. formed as a sn rface of revolution whereofmeans of revolution is coaxial with said land and with the entry throatand whereof the generatrix is an arc having a greater radius ofcurvature be ginning adjacent the land than adjacentthe entry throat.

2. A piston as claimed inclaim 1 wherein the generatriK is p t on Q s ra3. A piston as" claimed in claim 1 wherein the are which is'thegeneratrix of the cavity wall has two por-v tions, each portion beingpart circular and the portions having different radii of curvature, thecentre of cnrva: ture. of the larger radius portion being offset fromthe axis of revolution by'an amount equal'to' its radius, and thecentres of curvatureof the two portions being spaced apart by a distanceequal to the difference of the radii of curvature so that the "smallerradius portion is a continuation of the outer end of the larger radiusportion, the smaller radius portion forming at least thatv portion ofthe cavity wall immediatelysurrounding the end of the entry throat whereit opens into. the cavity, and the larger'radius part forming a portionat least of the cavity wall opposite the orifice.

4. A piston as claimed in claim 3 wherein the apex of the peaked land isat a distance of substantially twofifths ofthe radiusof .the largerradius pprtionbelow the plane containing the loci of the centres of thetwo parts oft hea rc. Y i i} i I 5. A piston as claimed inclaim 1wherein the ratio of the diameter of the narrowest part of the'entrythroat to the diameter of the piston lies in the range 0.15:1 to 0.25:1.

6. A piston as claimed in claim 1 wherein entry throat has a final entryportion which. is tapered to be part of a cone having an apex angle ofabout 15.

7. An internal combustion engine piston having a piston head, whereofthe end surface attords. the crown of the piston, said piston headhaving formed therein a recess open to the crown of the piston, saidrecess having a threaded wall portion adjacent the crown, a second ll pon a th n of h t aded W? q tiqa I?- mote from the crown formed as anannular abutment facing towards the crown, and a third wall portionforming the end of the recess remote from the crown, said third wallportion being formed as a surface of revolution whereof the generatrixis substantially a first circular are beginning adjacent the land andwhereof the axis of revolution is coaxial with the threaded wall portionand annular abutment, the centre of curvature of the first circular arebeing ,co-planar with the annular abutment and being offset from saidaxis of revolution thereby to form a peaked land coaxial with the recessprojecting towards the crown ,ofthe piston, a threaded s rt n sin aidthr ad d Wa Portion it O e end level with the crown of the piston and1ts-inrienend ut s d ula abl fl sa sai having an ine utt r t -m' t rbt ii a-r was of revolution whereof the generatrix is substantially a secondcircular arc having a smaller radius of curvature than the firstcircular arc and whereof the axis of revolution is coaxial with saidrecess; the centre of curvature of the second circular are being in theplane of said annular abutment and being offset from the axis ofrevolution by a distance which is greater thanthat by which the centreof curvature of .the first circular arc is offset, the two said centresof curvature being spaced apart by an amount equal to the difference ofsaid radii of curvature so that the two arcs form a smooth continuationof each other, said third wall portion of the recess and the innersurface of the insert together .defining a combustion cavity, and theinsert having formed therein an entry throat coaxial with said land andof circular section, the throat being open at one end to the crown ofthe piston and at its opposite end to the cavity, said throat taperingfrom the crown to the cavity and said second circular are having an endportion adjacent said entry throat, which end portion extends in adirection towards the peaked land and defines a lip projecting into thecavity round said opposite end of the entry throat.

8. A 'piston as claimed in claim 7 wherein the insert is formed from amaterial having a high resistance to heat.

9. A piston as claimed in claim 7 wherein the insert is coated'with amaterial having a high resistance to heat.

10. An internal combustion engine piston having a piston head, whereofthe end surface affords the crown of the piston said piston head havingformed therein a substantially cylindrical recess with a threaded wall;a cylindrical insert is disposed in the bottom of the recess, the inserthaving its end-face nearer the crown of the piston affording an annularabutment surface and within the annular abutment surface being formed asa surface of revolution whereof the generatrix is substantially a firstcircular arc and whereof the axis of revolution is coaxial with theabutment surface, the centre of curvature of the circular arc beingsubstantially co-planar with said abutment surface, and being offsetfrom said axis of revolution thereby to form an upstanding landprojecting towards the crown of the piston coaxially with saidcylindrical recess; and a threaded insert which is engaged with thethreaded wall and abuts said annular abutment surface, the threadedinsert having an inner surface remote from the crown formed as a surfaceof revolution whereof the generatrix is substantially a second circulararc having a smaller radius of curvature than the first circular arc andwhereof the axis of revolution is coaxial with the cylindrical recess,the centre of curvature of the generatrix of said inner surface beingcoplanar with the annular abutment surface and being offset from theaxis of revolution by a distance which is greater than that by which thecentre of curvature of first circular arc is offset, the two saidcentres of curvature being spaced apart by an amount equal to thedifference of the radii of curvature so that the two arcs form a smoothcontinuation of each other, said sur-,-

faces of revolution of the inserts together defining a combustioncavity, and said threaded insert having formed therein an entry throatcoaxial with cylindrical recess and of circular section open at one endto the crown of the piston and at its opposite end to the combustioncavity, said throat tapering from the crown to the cavity, and saidsecond circular are having an end portion adjacent said entry throat,which end portion extends in a direction towards the peaked land anddefines a lip projecting into the cavity round said opposite end of theentry throat.

11. A piston as claimed in claim 10 wherein the bottom of the recess isformed with a peripheral seating land for said cylindrical insert.

12. A piston as claimed in claim 11 wherein the upstanding land isprovided with a mushroom-shaped head,

serts are formed from a material having a high resistance to heat.

14. A piston as claimed in claim 10 wherein the inserts are coated witha material having a high resistance 15. Internal combustion enginepiston having a piston head, whereof the end surface affords the crownof the piston, a combustion cavity inthe piston head, an entry throat ofcircular section open at one end to the crown of the piston and at itsopposite end to the cavity, said throat tapering from the crown to thecavity whereby gases entering the combustion cavity are accelerated intheir passage through the throat, said cavity having its wall oppositethe entry throat formed with a peaked land which projects towards theentry throat coaxially therewith, the wall of the cavity being formed asa surface of revolution whereof the axis of revolution is coaxial withsaid land and with the entry throat and whereof the generatrix is an arehaving a greater radius of curvature adjacent the land than adjacent theentry throat, said are having an end portion adjacent the entry throat,which end portion extends in a direction towards the peaked land anddefines a lip projecting into the cavity round said opposite end of theentry throat.

16. An internal combustion engine piston having a piston head, whereofthe end surface aifords the crown of the piston, said piston head havingformed therein a recess open to the crown of the piston, said recesshaving a threaded wall portion adjacent the crown,a sec ond wall portionat the end of the threaded wall portion remote from the crown formed asan annular abut= ment facing towards the crown, and a third wall portionforming the end of the recess remote from the crown,

, said third wall portion being formed as a surface of revolutionwhereof the generatrix is substantially a first circular arc and whereofthe axis of revolution is coaxial with the threaded wall portion andannular abutment, the centre of curvature of the first circular arebeing co-planar with the annular abutment and being offset from saidaxis of revolution thereby to form a peaked land coaxial with the recessprojecting towards the crown of the piston, and a threaded insert madeof ceramic material engaging said threaded wall portion with its outerend level with the crown of the piston and its inner end abutting saidannular abutment said insert having an inner surface remote from thecrown formed as a surface of revolution whereof the generatrix issubstantially a second circulararc having a smaller radius of curvaturethan the first circular arc and whereof the axis of revolution iscoaxial with said recess; the centre of curvature of the second circulararc being in the plane of said annular abutment and being offset fromthe axis of revolution by a distance which is greater than that by whichthe centre of curvature of the first circular arc is offset, the twosaid centres of curvature being spaced apart by an amount equal to thedifference of said radii of curvature so that the two arcs form a smoothcontinuation of each other, said third wall por tion of the recess andthe inner surface of the insert together defining a combustion cavity,and the insert having formed therein an entry throat coaxial with saidland and of circular section, the throat being open at one end to thecrown of the piston and at its opposite end to the cavity, said throattapering from the crown to the cavity and said second circular arehaving an end portion adjacent said entry throat, which end portionextends in a direction towards the peaked land and defines a lipprojecting into the cavity round said opposite end of the entry throat.

17. An internal combustion engine piston having a piston head, whereofthe end surface affords the crown I 7 oi the piston said piston headhaying formed, therein a substantially cylindrical recess with athreaded wall; a cylindrical insert is disposed in the bottom of therecess; the insert having its end-face. nearer the crown of ,the

P st n afi rding n ann lar butm nt surface and within the annularabutment surface being formed as asuriace of revolution whereof thegeneratrix is substantially a firs i ular a c an whereof the axis ofrevolution .is coaxial with the abutment surface, the centre of curva:ture of the circular arc being substantially co planar with saidabutment surface, and being offset from said axis of revolution therebyto form an upstanding land p oj ng to a d h row of. the P s on. x allywith aid yl ndri l ecess; an a thr a e nsertmad of ceramic materialwhich is engaged with the threaded wall and abuts said annular abutmentsurface, the threaded insert haying an inner surface remote from the'croWn formed as a surface of reyolution .Whel'fiQf the generatrix issubstantially a second circular arc have a m er rad us o u va ure h nthffirstcireular arc and whereof the axis of reyolution is coaxial withthe cylindrical recess, the centre of curvature of the gen: a x o sai ner ur ace e n copl na w th he annular u e su a e. nd. b ng. fliset rs nh axi of revolution by a distance which is greater than that by whichthe centre of curvature of first circular arc is other, the two s id cenres flsuwflme being spaced apart by. an amount equal to the difierenceof the radii of curvature so that the two arcs form a smoothcontinuation of each other, said surfaces of revolution of the insertstogether defining a combustion cavity, and said r ad d ns avin a med hre an ntry throat coaxial with cylindrical recess and of circularsection open at one end to'the crown of the piston and'at its oppositeend to the combustion cavity, said throat tapering frsm e QW t h a itand said nsed circular are having an end'portion adjacent said entrythroat, which endportion extends in a. direction towards peake a d n dfines p p oisst ne ts the cavity round said opposite end of the entrythroat.

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22- Apis sn. s l med in slain? 5 WhsIsi h entry throat has a final entryportion which is tapered to be p t at a. ne ha in as an??? ea le s ahout15 fi fs n ss Ci e .i t file of this e UNITED STATES PATENTS-

